It is known, in general, in the prior art to coat metal surfaces with various phenylene oxide polymers to form coatings which provide some degree of corrosion protection to the metal surfaces.
Certain references suggest the use of electropolymerized polyphenylene oxides in corrosion resistant coatings including the following: M-C. Pham et al., Bull. Societe Chimique France 1985, 1169; M. Vijayan et al., Bull. Electrochemistry 1986, 2, 349; T. F. Otero et al., Makromol. Chem., Macromol. Symp. 1987, 8, 255; and S. Pitchumani et al., J. Electrochem. Soc. India 1990, 39, 211.
One approach that has been described utilizes the electrochemical deposition of various phenylene oxide polymers as coatings onto the metal by utilizing a solution containing the polymerizable phenol monomer(s). See, for example, Chemical Abstracts, Vol. 84, 181695h (1976) and Chemical Abstracts, Vol. 95, 188687t (1981).
An alternative approach to the foregoing electrochemical deposition techniques has relied upon the deposition of the prepolymerized PPO material onto the metal either from solution or as a powder coating:
In U.S. Pat. No. 3,455,736 to H. R. Davis et al., it is taught that certain types of PPO material are deficient in regard to their temperature or solvent resistance (see Col. 1, lines 35-47) and that such disadvantages can be remedied by the use of what is termed "certain linear or substantially linear" PPO materials. Such "selected polyphenyleneoxide oxide polymer" (see Col. 3, line 24) would, for example, not have alkyl group substitution on the arylene rings of the polymer and are formed from condensation reaction of potassium p-chlorophenolate.
More recent U.S. Pat. No. 3,907,613 teaches the use of a "substituted" PPO material, namely, 2,6-dimethyl-1,4-phenylene oxide, to coat metal surfaces, in violation of the teachings of the above described '736 patent. This patent indicates (at Col. 1, lines 13-21) that PPO films on metal lose their adhesion upon drying and are therefore "unsuitable to create protective layers on metal" unless expensive treatments of the metal with a thin layer of copper or silver are performed. As alternative approaches to such an expensive approach, this patent proposes either: (1) that the metal surface be provided with an oxidized conversion surface layer (see Col. 1, lines 28-33), such as by heating the metal (see Col. 1, lines 59-60); (2) that the PPO resin be modified by the inclusion of other resins and/or softening agents (see Col. 1, lines 34-37); (3) that corrosion inhibitor(s) be included in the PPO resin layer (see Col. 1, lines 39-45); or (4) that a further coating of PPO be used on top of the initial layer (see Col. 1, lines 46-49).